Hybrid rocket fuel and process of propulsion using tetraformaltriazine

ABSTRACT

Tetraformal-tris-azine is a high energy fuel material suitable for use in hybrid rocket motors either as a compound per se or admixed with suitable binders.

Unite States Vessel atet [ 1 May 23, 1972 [54] HYBRID ROCKET FUEL ANDPROCESS OF PROPULSION USING TETRAFORMALTRIAZINE [72] Inventor: Eugene D.Vessel, Santa Clara, Calif.

[73] Assignee: United Aircraft Corporation, East Hartford, Conn.

22 Filed: Feb. 1,1966

21 Appl.No.: 523,976

52 U.S.Cl ..60/220,l49/19,149/36, 60/219 51 1m.c|. ..C06d5/10 5sFieldofSearch ..60/219,220;149/36,l09,l8, 149/19, 20

Primary Examiner-Benjamin R. Padgett Attorney-Steven F. Stone [5 7]ABSTRACT Tetraformal-tris-azine is a high energy fuel material suitablefor use in hybrid rocket motors either as a compound per se or admixedwith suitable binders 4 Claims, No Drawings HYBRID ROCKET FUEL ANDPROCESS OF PROPULSION USING TETRAFORMALTRIAZINE BACKGROUND OF THEINVENTION This invention relates to hybrid fuel compositions and moreparticularly to tetraformal-tris-azine, hereinafter referred to as TFTA,as a primary hybrid fuel component.

As presently formulated, most hybrid fuels consist of an elastomericbinder containing various quantities of high energy ingredients, flametemperature modifiers, oxidizers and regression rate modifiers. Theseformulations comprised of various amounts of the above ingredientsgenerally are tailored to produce a hybrid propellant grain which has aparticular burning rate and flame temperature characteristic and anonsustaining characteristic such that the combustion will stop whenoxidizer flow is cut off.

Since it is generally desired to optimize the performance of a hybridmotor, it is preferable to employ as much of the high energy componentas possible while keeping the binder, which is generally a fairly lowenergy material, to that minimum amount required to impart the desiredphysical properties to the grain. Much work is presently being done inthe development of such high energy fuel components and at present, twoof the most promising components are known to workers in the art as TAZand THA. While both of these materials have high specific impulses, theyare extremely expensive and exhibit impact sensitivity.

TFTA has been found to have a specific impulse comparable to that ofhydrazine. For example, a TFTA-N 0. system with an O/F ratio of 2, has atheoretical specific impulse of 283 seconds. In addition, TFTA isreadily prepared from commercially available materials and therefore issubstantially less expensive than TAZ or THA. TFTA is clean burning, haslower impact sensitivity than either TAZ or THA and is sensitive tovariations in chamber pressure and oxidizer flow rate so that it isparticularly useful in a throttleable hybrid system.

Accordingly, it is an object of this invention to provide a novel hybridrocket fuel consisting ofTFTA.

It is another object of this invention to employ TFTA as a component ofahybrid rocket fuel.

It is another object of this invention to provide a process foroperating a hybrid rocket motor wherein TFTA is a fundamental fuelcomponent.

It is another object of this invention to provide a smokeless hybridrocket fuel.

These and other objects of the invention will be readily apparent fromthe following description.

DESCRIPTION OF THE INVENTION TFTA has the following structural formula:

The material itself is readily prepared by reaction of formaldehyde andhydrazine as follows:

4CH O 3N H CJI N 4H,O (TF TA) The synthesis of TFTA is reported in thefollowing literature references: R. Stole, BER 40, 1,505, (1907) and K.l-Iauffman and D. Storm, BER 45, 1,728, (1912).

TFTA basically can be formed by reacting an aqueous solution offormaldehyde and hydrazine at room temperature. The solution is allowedto stand several days, the TFTA separates as white needles which can bereadily recovered. TF1 A has a heat of formation of +83.9 t 1.5 K calper mole and a heat of combustion equal to 6.033 t 0.012 K calorie pergram as determined by oxygen bomb calorimetry. The melting point of TFTAis 245 C. and has a density of about 1.3 grams per cubic centimeter.

Impact sensitivity experiments indicate that TFTA is substantially lesssensitive to impact than TAZ or TI-IA. This fea ture enhances theattractiveness of using TFTA as a hybrid fuel material. TFTA can be usedas the sole fuel component for a hybrid rocket grain or it can be usedas an additive in hybrid rocket grains comprising elastomeric bindersand one or more combustion modifiers. Suitable binders includepolybutadiene polymers, particularly hydroxyl terminated polybutadienescured with toluene diisocyanate for example, polyethers such as amineterminated polyethers cured with epoxy resins and silicone rubbers suchas polydimethylsiloxane cured with an organometallic cure catalyst suchas dibutyl tin dilaurate. If a grain is to be formulated by compactingTFTA, a particulate binding agent such as polyethylene or polypropylenecan be incorporated into the grain to enhance the physical properties ofcompacted grains.

Suitable flame temperature modifiers include powdered metals such asaluminum, boron, magnesium and alkali metals. Other materials such assolid oxidizers, for example ammonium perchlorate and ammonium nitrateand various burning rate controlling agents such as iron oxide, chromicoxide and ferrocene compounds can also be employed as is well known inthe propellant art in formulating the grain according to this invention.

TFTA can be employed as the sole ingredient of a hybrid rocket fuelgrain, in which case, it is compacted into the form of the grain bypressing for example with or without a binding agent and then utilizedin the hybrid motor. TFTA can be used as an additive with various of theabove hybrid fuel components. In general, the amount of TFTA employedcan vary from below one percent on up to the maximum amount that can bephysically incorporated within the binder system under consideration.This maximum value varies with various binder systems and is notcritical. The highest solid loading so far obtained is about percent byvolume, but this figure should not be construed as being the upper limitof usefulness of the material. It is expected that other binder systemswill be developed that will permit higher solids loadings and as such isthe case, even higher ranges of TFTA can be included in the systems. Inany event, it is preferable to have more than 25 percent by volume ofTFTA in the system.

The following examples are representative of the use of TFTA accordingto this invention:

EXAMPLE 1 487 grams of a 37 percent solution of formaldehyde in waterwas added dropwise to 200 grams of a 75 percent solution of hydrazine inwater over a period of 4 /2 hours. The reaction mixture was kept at 50C. Solid TF1 A separated upon cooling of the mixture.

EXAMPLE 2 EXAMPLE 3 A hybrid fuel grain was formulated by mixing 45weight percent TFTA with 55 percent of an hydroxyl terminatedpolybutadiene-toluene diisocyanate binder at 70 F. A propellant grainwas cast and cured satisfactorily at F. for 18 hours.

EXAMPLE 4 A propellant grain having the following formulation wassatisfactorily cast and cured at F. for 18 hours:

Ammonium Perchlorate TFTA Aluminum Powder Hydroxyl TerminatedPolybutadiene cured with Toluene Diisocyanate 35% EXAMPLE 5 Thefollowing composition was cast into a hollow hybrid grain 6 inches longand having a diameter of 0.75 inch.

TFTA 35% Aluminum 5% Carbon Black 1% Hydroxyl Terminated Pnlyhutadiene54.39% 'lnluenc Diisocyanate 4.61%

The grain was tired with oxygen for 2.57 seconds in a motor having anozzle diameter of 0.250 inch. A chamber pressure of 1,000 psig wasobtained and 33.18 grams of propellant was burned.

EXAMPLE 6 A suitable pelletized hybrid fuel system is represented by thefollowing composition:

29.59% Boron 1.23% Carbopol 14.58% TFTA 61.64% 20.57% Ammonium 4 1.15%Boron Perchlorate 80667 38.36% 29.37%TFTA 30.75% Boron 100.00%

While this invention is described with respect to several specificexamples thereof, the invention should not be construed as being limitedthereto. Various modifications and substitutions can be made withoutdeparting from the scope of this invention which is limited only by thefollowing claims:

lclaim:

1. In a process for operating a hybrid gas generator which comprisescombusting a solid fuel grain in a combustion chamber by means of afluid oxidizer and exhausting the combustion products produced therein,the improvement wherein said grain comprises tetraformaltrisazine.

2. In a process for operating a hybrid rocket motor which comprisescombusting a solid fuel grain in a combustion chamber by means of afluid oxidizer and exhausting the combustion products produced through athrust producing nozzle, the improvement wherein said grain comprises acompatible elastomeric binder and tetraformaltrisazine.

3. A hybrid rocket fuel grain comprising tetraformaltrisazine dispersedwithin a compatible polymeric binder.

4. The hybrid rocket grain of claim 3 wherein said tetraformaltrisazineis present in amounts above 25 percent by volume.

2. In a process for operating a hybrid rocket motor which comprisescombusting a solid fuel grain in a combustion chamber by means of afluid oxidizer and exhausting the combustion products produced through athrust producing nozzle, the improvement wherein said grain comprises acompatible elastomeric binder and tetraformaltrisazine.
 3. A hybridrocket fuel grain comprising tetraformaltrisazine dispersed within acompatible polymeric binder.
 4. The hybrid rocket grain of claim 3wherein said tetraformaltrisazine is present in amounts above 25 percentby volume.